Well, I don't recall ever seeing one of these before, so I thought I'd start it.
A while back I found a can of Great Stuf - and for those of you who don't know, it's canned foam that expands and just happens to be not only flammable, but highly combustible as well. Anyway, the can was almost full, but it was rusty and old so I decided to set it on fire for the pure hell of it (I'm a bit of a pyromaniac). SO... I sprayed some of it into the burn barrel in my back yard, tossed the can in as well, pulled out my trusty Bic, and FWOOM! The stuff went off like a cannon. It dented the barrel with the first blast, which was just the foam I sprayed, and when the can actually burst it damn near blew a hole in the barrel. Scared me half to death, but it was well worth it. Awesomest show I've ever seen, flames twenty feet high shooting out of the barrel. Kids, don't try this at home.